Single tube FM transmit circuit ----- fm Transmitter

Single tube FM transmit circuit, FM Transmitter Keywords: single tube FM transmit circuit Single tube frequency modulation circuit This circuit is 1.5km single tube frequency modulated transmitter circuit. The transmitting triode is employed by D40, D50, 2N3866, and the operating current is 60 to 80 mA. But the above triodes is difficult to purchase, and the price is high, and there are many fakes. The author chooses other triode experiments, relatively priced trioders C2053 and C1970 are quite good, and the actual distance communication distance is greater than 1.5km. The author also replaced D40 to ordinary triode 8050, and the working current is 60 ~ 80mA, but the emission distance is less than 1.5km. If the transmission is changed to 9018, the working current is smaller, and the emission distance is also shorter. In addition to the transmitting tripod, the parameters of the coil L1 and the capacitor C3 are more important. If the selection is not properly selected or the operating frequency exceeds 88 to 108 MHz range. Among them, L1, L2 can be used in a rod of 3.5 mm, a single layer, 5 hints and 10, C3, and C3 selected from 5 to 20 pF, a porcelain or polyester adjustable capacitor. When actually made, the capacitor C5 may be omitted, and the L2 can also be replaced with a normal inductor coil of 10 to 100 MH. If the emission distance is tens of meters, then the battery voltage can be selected from 1.5 to 3V, and the D40 tube is replaced with a cheap 9018, etc., and the power consumption will be less. The single tube transmitter introduced in Figure 1 has a simple circuit, the output power is large, and the production is easy to make, but it is inconvenient to send a high frequency cable to transmit the RF signal to the outdoor transmission antenna, which is generally a rod antenna of 0.7 ~ 0.9m. Directly in C5, due to the Doppler effect, people move in the vicinity of the antenna, the frequency drifting is very serious, making the sound of the receiver that the radio is normal, distortion or silent. If the transmitter is used as a wireless microphone, when the antenna is pinched, it can be imagined. The circuit uses a capacitor three-point oscillator. When the antenna parameter is slightly changed, it will have a running frequency, and then, since the single tube self-excited oscillation is transmitted, the working current is large, when the working number of seconds to several minutes, the temperature of the triode Elevation causes a change in pole capacitance to change the oscillation frequency (in general, the oscillation frequency is lowered), and sometimes the float is from 0.2 to 1 MHz. It is poorly reliability when used as FM broadcast or long-distance remote alarm, but the components are less, low cost, and easy to debug, suitable for primary enthusiasts.